Various types of floating docks are available that are assembled from modular elements to enable ease of assembly and portable use. Portable docking systems are used in northern climes where they ordinarily are removed from the water and stored during the winter.
Rubinsak et al. in U.S. Pat. No. 4,988,317 discloses a sectionalized float which can be disassembled and stacked for storage. A deck is braced by a grid; a large-scale egg-crate of two-by-four lumber for example. Within the grid are fastened the lids of large, screw-top containers such as five gallon plastic buckets. These are removably screwed onto the lids to form individual, sealed floats to comprise a pontoon. A means to join pontoons is provided to form complex floating structures.
In U.S. Pat. No. 3,191,565, Filak teaches the use of post-tensioned cables to hold together a complex of float units.
In U.S. Pat. No. 3,323,479, Filak teaches using ballast tanks for stability in a flotation module.
In U.S. Pat. No. 3,673,975, Strauss teaches a floating platform that includes a plurality of air cells to support a platform. The cells comprise a heavy gauge polyethylene sheeting pursed and inverted so that air can not escape. The bottom thus is open to the water. Means for subsequent addition of air is also described as is a skirting around the edge of the platform.
Northam et al., in U.S. Pat. No. 5,117,775, teaches a flotation device in which the hollow interior of a molded shell is filled with recycled, sealed plastic bottles. These are layered and oriented and aligned end to end or are disposed with the neck of one lying adjacent the neck of its neighbor. The shell has indentations to accommodate the necks and may be filled with a foam material. The bottles may be detachably bonded for ease of orderly loading or may be randomly placed. The shell may be sealed or have an opening to permit ballast water to enter. The bottles are not disposed to be structural, load-bearing elements and the shell/bottle combination is not disposed to be a dock structure in itself.
Floating docks of the prior art are float and beam devices. In essence the deck is a beam structure which is supported by one or more separate flotation means. A concentrated load on the deck must be carried by the deck beams to the floats. The beam structure must be of sufficient size and stiffness and therefore weighs an excessive amount given the use of standard materials.
The prior art beam and float units do not use the materials of construction in an efficient way. If the floats were closer together, however, the deck could be of lighter construction. Also, if the floats were both close and fused together (i.e. unitary) they could act also as stiffeners to the deck and the deck could be of the lightest construction.
In U.S. Pat. No. 3,824,644, Stranzinger teaches the use of prismatic flotation bodies that have protruding lugs which can be mated using connecting bolts to produce a connected flotation structure.
In U.S. Pat. No. 4,604,962, Gibault teaches the use of similar prismatic flotation bodies joined together to form a dock.
Both Stranzinger's and Gibault's teachings attach the floats together so that they can pivot at their joints. Flexure stresses are not carried from float to float since they are not attached as an integral, unitary structure. Additionally, there is no continuous upper deck structure to act as the upper (beam) flange nor is there a lower continuous sheet, or its equivalent, to act as the bottom flange. Again, these jointed structures do not use the materials of construction in an efficient manner
Commercial modules are available fabricated from wood and drum floats, and a variety of high density polyethylene pontoons or slabs used as flotation elements in combination with wooden or metal structural materials. Many of these form beam structures. These units are effective but suffer from limitations. Either the modules are too heavy for easy portability or, to achieve a readily handled module, they are too small which makes the platforms unstable when people stand on them and when the waves set the assembled modules in motion. Other problems include cost and also corrosion where wood and metal are employed.
It is an object therefore of the instant invention to overcome the shortcomings of the prior art and to provide flotation modules that are of integral, unitary structure and so are lightweight, low cost, and truly portable in being easy to get on and off the water.